Conventional paddles or oars for facilitating human-powered propulsion of small watercraft such as row boats, canoes, kayaks, and the like, are typically constructed from a tubular shaft with a broad, flat blade at one or both ends thereof. Oars are attached via a pivot to the watercraft and are operated as levers, whereas paddles are held in the operator's hands during use. For the sake of simplicity, where no distinction is meant to be conveyed between paddles and oars, the term “paddle” shall be used hereinafter to refer to either one. Similarly, the actions of paddling and rowing shall be referred to simply as “paddling” where no distinction therebetween is meant to be conveyed.
The shaft and the blade can be integrally formed, as in the case of classical canoe paddles that are made from a single piece of wood; or can be assembled from a plurality of parts using different materials for the various components. For example, some conventional paddles have a lightweight shaft made from aluminum tubing with one or two paddle blades at one or both ends made from a hard plastic material.
Most often, the blades used in paddles or oars are constructed from a rigid, inflexible material that mostly retains its shape during paddling. Accordingly, for these types of paddles, any deformation of the blade as a result of the interaction forces between the blade and the water during paddling is marginal at most. When a hard, non-compliant paddle blade is drawn through the water during paddling, the paddle blade face pushes water in a direction opposite the direction in which the watercraft is to be propelled. Much of the water against which the paddle blade presses flows over the face of the paddle blade towards its edges, and past its edges. The water flowing over the face of the paddle blade flows from a relatively high-pressure zone at the face of the blade to a relatively low pressure zone past the edge of the blade. This flow is turbulent, and the pressure change creates eddy currents in the wake of the paddle stroke. The turbulence and eddy currents are a source of energy loss due to some of the paddling energy being taken up by the mixing, internal friction, and whirling of the water.
In some paddles, the paddle blade is designed to deform to some extent by virtue of the material from which the blade is formed. This type of deformation may be useful to prevent breakage of the blade that might occur when the blade strikes a rock or other hard object during use. However, deformation resulting from water pressing against the paddle blade's face during paddling in these types of paddles dissipates some of the paddling energy, thereby presenting an inefficiency. Additionally, flexible paddle blades suffer from the energy loss associated with the turbulence and eddy currents described above.
There have been various paddle designs proposed to improve paddling efficiency. U.S. Patent Application Publication No 2010/0009580 (Gomez Escobar) discloses a flexible oar having a blade with a hard edge and a soft, resilient, flexible core that stretches to create a pocket of water during rowing, thereby increasing the surface in contact with the water. However, the proposed design creates a turbulent flow that spills over all of the edges of the pocket, resulting in mixing and internal friction in the water, and eddy currents in the oar blade's wake.
U.S. Pat. No. 4,303,402 (Gooding) discloses a paddle with a cup-shaped blade displaced at an angle relative to the shaft for increased efficiency. The paddle blade has sidewalls that tend to scoop water like a spoon. However, the paddle blade maintains a constant non-flat shape, which presents additional drag against the water while the paddle is raised and lowered into the water during paddling. Moreover, as with the Gomez Escobar paddle design, water spills over the sidewalls during paddling, which creates turbulence and eddies.
U.S. Pat. No. 6,814,640 (Houck) discloses swimming fins having a web portion with a plurality of support members. The fins are designed such that their shape changes as the swimming action alternates between the power stroke and return stroke. As with all fins, they are used entirely underwater (i.e. not removed and re-inserted as with paddling), with the major fin surfaces being oriented generally parallel to the direction of travel. Flexure of the fins is designed to force water in the backwards direction, so the fins are generally made to be rather soft. These characteristics make fin designs generally unsuitable for use as paddle blades, since the latter are designed to exert a force against the water while the blade is oriented generally perpendicularly to the direction of travel.
U.S. Pat. No. 4,302,194 (Perales) discloses a combined propulsion and support device for a swimmer. The device is designed with a pair of opposing paddle blades on opposite ends of diametrically opposed tubular arms, with a flotation device in the center. The swimmer holds on to the arms, and paddles with the blades in alternating fashion. The paddle blades are triangular in shape and are slidably mounted in the arms and are constructed with ribs and webs extending therebetween. The ribs and web are designed to permit the blades to collapse and slide into the arms. The combined propulsion and support device is geared to work with an individual swimmer moving at a relatively slow speed. The design of the device does not provide a solution for efficient propulsion of watercraft, which have a greater mass and speed of travel far in excess of the individual swimmer. Particularly, the flexibility of the ribs needed to facilitate collapsibility into the arms, and the slidable arrangement of the blades inside the arms, provide a non-rigid, spring-loaded coupling between the paddle blades and the arms. While paddling, movement of the blades relative to the arms, and the associate friction, dissipate applied energy and make the device unsuitable for use in propelling watercraft efficiently.
Although these, and various other attempts have been made to improve the efficiency, portability, and storage of aquatic propulsion devices, each has its own drawback that results in either a compromise of performance, or makes the approach unsuitable for use with watercraft that are paddled or rowed.